1. Field of the Invention
The present invention relates to an intake system for introducing intake air into an internal combustion engine, and more particularly to an intake system having an amount-of air detector for detecting an amount of intake air introduced into an internal combustion engine.
2. Description of the Related Art
Internal combustion engines that have been used on motor vehicles or the like have intake pipes for introducing intake air into the cylinders which provide combustion chambers and intake valves mounted in respective intake ports, to which the respective intake pipes are connected, for selectively bringing the cylinders into and out of fluid communication with the respective intake pipes. When the intake valves are opened, intake air is introduced through the intake pipes into the cylinders.
Intake pipes disclosed in Japanese Laid-Open Patent Publication No. 2004-190591, for example, are connected to a throttle valve for regulating the rate of intake air (amount of intake air) flowing through the intake pipes. The valve opening of the throttle valve is adjusted to regulate the amount of intake air introduced into the cylinders. An air flow sensor, for measuring or detecting the amount of intake air flowing through the intake pipes, is disposed upstream of the throttle valve. A surge tank is connected to the intake pipes downstream of a throttle body and has a pressure sensor for detecting the air pressure in the intake pipes.
A detected signal from the air flow sensor is output to a control circuit, which calculates the amount (mass or volume) of intake air introduced into the cylinders from the detected signal from the air flow sensor. Then, the control circuit calculates an optimum amount of fuel to be injected into the cylinders depending on the operating state of the internal combustion engine based on the calculated amount of intake air. The control circuit then outputs a control signal representing the calculated optimum amount of fuel to a fuel injector, thereby controlling operation of the fuel injector.
According to the above conventional intake system, when the throttle valve is quickly opened to rapidly accelerate the motor vehicle, intake air for filling the surge tank connected to the intake pipes that are under a negative pressure is introduced into the intake pipes, in addition to the intake air that is actually introduced into the cylinders. Therefore, the amount of intake air that is detected by the air flow sensor is the sum of intake air actually introduced into the cylinders and part of intake air filling the intake pipes.
The pressure sensor that is disposed downstream of the throttle valve separately from the air flow sensor detects the pressure of intake air in the intake pipes, and the control circuit estimates the amount of intake air filling the intake pipes. The control circuit is required to subtract the estimated amount of intake air from the total amount of intake air detected by the air flow sensor, thereby estimating the amount of intake air that is actually drawn into the cylinders for controlling the internal combustion engine.
With the above conventional intake system, however, the amount of intake air drawn into the cylinders is estimated based on the amount of intake air detected by the air flow sensor disposed upstream of the throttle body and the pressure detected by the pressure sensor. Consequently, the control system fails to accurately recognize the amount of intake air actually introduced into the cylinders, and finds it difficult to accurately control the amount of fuel injected into the cylinders based on the amount of intake air.